1. Field of the Invention
This invention relates to an image sensing device with a wide substantial dynamic range.
2. Description of the Related Art
Image sensing devices are being widely used, for example, as the video camera sections of video tape recorders with integrated cameras or as still video cameras. A video camera using an image pick-up tube or a solid image sensing element has a relatively narrow dynamic range as compared with the conventional silver halide photography system, so that it is subject to generation of white blankings and blackenings (common names for portions with excessively high or low luminance) under back light conditions. In conventional video cameras, adjustment of the quantity of light in such cases is effected by opening the diaphragm two steps or so, either manually or with a backlighting compensation button.
However, even when such backlighting compensation is appropriately conducted, with the main subject being properly exposed, white blankings may be generated in the background, leaving the picture with a blank background. In other words, the narrowness of the dynamic range in an image sensing device cannot be overcome merely by adjusting the quantity of light to attain a proper exposure for the main subject, as in the case of conventional devices. To cope with this, an improvement has been proposed in the conventional image sensing device of the type in which a still image is transduced into an electrical signal by means of a line scanner or the like. According to this improvement, a plurality of images of different exposures obtained from the same subject are combined to compose a single picture. Similar ideas are disclosed, for example, in U.S. patent application Ser. No. 792,768 and Japanese Laid-Open Patent Application No. Sho 61-219270.
However, they are directed to still images and are not capable of providing a moving picture with a wide dynamic range.
In view of this problem, it is an object of this invention to provide an image sensing device which has a wide substantial dynamic range and which makes it possible to obtain moving pictures.
Another object of this invention is to provide an image sensing device which permits the exposure control and focusing control to be conducted in an appropriate fashion.
To attain the above objects, an embodiment of this invention comprises image sensing means, control means adapted to cause a plurality of pictures of different exposures to be output successively from the image sensing means and composition means adapted to combine pictures with different exposures from among the ones output from the image sensing means to compose a moving picture.
This construction makes it possible to obtain a plurality of images of different exposures successively, so that by effecting the composition by means of the composition means in a time less than the time between successive video frames, composed moving picture of a proper exposure can be obtained. The speed of the composition operation performed by the composition means can be set sufficiently high, so that there is no problem in this regard.
Another embodiment of this invention consists of an image sensing device adapted to compose an appropriate single picture out of a plurality of pictures of different exposures obtained from the same subject, the image sensing device being characterized by the fact that the camera operation is controlled using a signal indicative of one of the plurality of pictures of different exposures as the reference signal.
The control operations for the camera such as the exposure control and focus adjustment are thus conducted using the signal indicative of one of the plurality of pictures of different exposures as the reference signal, whereby correct camera operation can be assured, without any destabilization thereof.
A further embodiment of this invention consists of an image sensing device adapted to obtain an appropriate picture out of a plurality of images of different exposures obtained from the same subject, the image sensing device being characterized by the fact that the processing of the target picture element is effected taking into consideration the information on the picture elements around the target picture element.
This device thus provides a dynamic range which substantially includes the plurality of images of different exposures, so that it can give a satisfactory image both of the main subject and the background. Further, the number of isolated points is reduced by processing the target picture element taking into consideration the information on the picture elements around the target one, whereby a more correct distinction is attained between the main subject and the background.
A still further embodiment of this invention consists of an image sensing device comprising image sensing means, a control means adapted to cause video signals indicative of a plurality of pictures of different exposures obtained from the same subject to be output from the image sensing means, an image memory capable of storing some of the video signals indicative of the plurality of pictures output from the image sensing means and arithmetic processing means which is adapted, whenever the signal of a target picture element on any picture is judged to be inappropriate, to select or process signals indicative of a plurality of other pictures corresponding to the target picture element to generate an output picture element signal.
Thus, by causing video signals indicative of a plurality of pictures of different exposures to be output from the image sensing means and storing the video signals temporarily in the image memory, it is made possible to discriminate the picture elements of an appropriate exposure from those of an inappropriate one and to replace the picture elements of an inappropriate exposure with the picture elements of an appropriate one by replacing the video signal of the former with the corresponding signal of a picture taken under a satisfactory exposure. Consequently, an appropriate image can be obtained over a wide exposure range, which means that the dynamic range of the image sensing means has been substantially enlarged.
A still further embodiment of this invention consists of an image sensing device equipped with an image sensing means which is adapted to output image sensing signals of different charge storage times by switching for each field and that is characterized by the fact it composes a single picture out of successive pictures of two fields.
By thus composing a picture of image sensing signals of different charge storage times, an image sensing signal of a substantially wide dynamic range can be obtained.
A still further embodiment of this invention consists of an image sensing device for obtaining a single picture out of a plurality of pictures of different exposures derived from the same subject by a switching operation, the image sensing device being characterized in that a single picture selection color signal is generated from a plurality of picture selection luminance signals and based on said single picture selection color signal, color signal data are selected.
By thus composing a picture of image sensing signals of different charge storage times, an image sensing signal of a substantially wide dynamic range can be obtained.
A still further embodiment of this invention consists of a method of controlling an image sensing device provided with a first image sensing mode in which light storage operations of n seconds duration are repeated to form a video signal and a second image sensing mode in which n-second light storage operations and m-second light storage operations (m being less than n) are alternated to form a video signal for a single picture, the controlling method being characterized in that a switching signal for the first and second image sensing modes and a picture element composition control signal for the n-second storage pictures and m-second storage pictures in the second image sensing mode are formed out of the n-second storage pictures.
By thus forming out of the n-second storage pictures in the normal first image sensing mode a switching signal for the first and second image sensing modes and a picture element composition control signal for the n-second storage pictures and the m-second storage pictures in the second image sensing mode, a first image sensing mode with no deterioration in the time resolution is selected, and the picture element composition in the second image sensing mode is made as free from deterioration of time resolution as possible.
Further objects and features of the present invention will be apparent from the following description and drawings.